The present invention relates in general to molding materials for protecting the stators of submersible motors, and in particular to a molding material having a lower moisture permeability than conventional molding materials for submersible motors.
FIG. 1 shows a simplified longitudinal cross-sectional view of the stator portion of a conventional submersible motor of the type to which the present invention is directed. In the figure, element 1 is a stator core, element 2 is the coil end portion of the stator coils for the stator core 1, element 3 is a stainless steel inner wall of a stainless steel casing (other parts of the casing not shown) which seals off the stator and protects it from moisture, element 4 is a molding material which fills all the empty spaces in the casing, and element 5 is electrical connections for the stator coils. That part of the motor lying inside the inner wall 3 is generally filled with an anti-freeze which serves to lubricate the thrust bearings (not shown) of the rotor (also not shown) of the motor.
The inner wall 3 is able to prevent anti-freeze, water, and other liquids from entering, via the rotor, the space around the stator. However, liquids are able to enter the motor from the ends of the casing or from connecting members via gap, between the inner wall 3 and the molding material 4, which form at the time of molding or thereafter. It is therefore important for the molding material to have a low permeability to moisture.
Materials commonly used for the molding material 4 include polyester resins and vinyl resins. However, such molding materials have the drawback that they are not sufficiently impermeable to moisture, and water is able to permeate the molding material 4 and reach the stator. This permeation results in an undesirable decrease in the insulating resistance of the molding material 4.
There is therefore a need for a molding material for use in the type of submersible motor illustrated in FIG. 1 which has a lower moisture permeability than presently used molding materials.